The primary objective of this study is to determine the rate at which recently acquired information is forgotten in patients with senile dementia of the Alzheimer's type (SDAT) and in patients with depression, as compared to normal elderly. Differences in decision strategy (i.e., willingness to guess) and learning efficiency among demented, depressed and normal elderly groups will also be explored and documented. The study is intended to further our understanding of the nature of memory disorder associated with dementia and depression and to establish an efficient, reliable procedure to be employed in the early diagnosis of SDAT versus depression and benign senile forgetfulness. Such a procedure may facilitate effective intervention strategies and aid in the evaluation of treatment procedures such as antidepressant medication and cholinergically active drugs. All subjects will undergo a routine evaluation prior to inclusion in the study, which will include a neuropsychological screening evaluation, neurological examination and structured psychiatric interview. Dementia and depressed patients will also have undergone an extensive workup to rule out focal lesions and other medical causes for suspected mental deterioration and normal elderly with evidence of systemic medical illness from exam or medical record information will be excluded. Subjects meeting diagnostic criteria will then be administered the rate of forgetting test in which recognition memory for line drawings of common objects will be tested at intervals of 10 minutes, 24 hours and 7 days. Signal detection analysis will be utilized to distinguish memory capacity and decision strategy. Stimulus exposure time will be determined for each group in order to equate performance at the 10-minute test interval and thereby control for group differences in learning efficiency. Patients with suspected dementia will be followed for a period of years at the Dementia Clinic at no cost to the study to further establish diagnoses and assess the validity of the rate of forgetting procedure. A clinical neuropsychologist, experimental psychologists, a psychiatrist boarded in neurology and a neurologist will collaborate.